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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 308673.0, MPI für Astronomie / Publikationen_mpia
Hot organic molecules toward a young low-mass star: A look at inner disk chemistry
Authors:Lahuis, F.; van Dishoeck, E. F.; Boogert, A. C. A.; Pontoppidan, K. M.; Blake, G. A.; Dullemond, C. P.; Evans, N. J.; Hogerheijde, M. R.; Jørgensen, J. K.; Kessler-Silacci, J. E.; Knez, C.
Date of Publication (YYYY-MM-DD):2006
Journal Abbrev.:The Astrophysical Journal
Start Page:L145
End Page:L148
Audience:Not Specified
Abstract / Description:Spitzer Space Telescope spectra of the low-mass young stellar object (YSO) IRS 46 (Lbol~0.6 Lsolar) in Ophiuchus reveal strong vibration-rotation absorption bands of gaseous C2H2, HCN, and CO2. This is the only source out of a sample of ~100 YSOs that shows these features, and this is the first time that they are seen in the spectrum of a solar-mass YSO. Analysis of the Spitzer data combined with Keck L- and M-band spectra reveals excitation temperatures of >~350 K and abundances of 10-6 to 10-5 with respect to H2, orders of magnitude higher than those found in cold clouds. In spite of this high abundance, the HCN J=4-3 line is barely detected with the James Clerk Maxwell Telescope (JCMT), indicating a source diameter less than 13 AU. The (sub)millimeter continuum emission and the absence of scattered light in near-infrared images limit the mass and temperature of any remnant collapsing envelope to less than 0.01 Msolar and 100 K, respectively. This excludes a hot-core-type region as found in high-mass YSOs. The most plausible origin of this hot gas rich in organic molecules is in the inner (<6 AU radius) region of the disk around IRS 46, either the disk itself or a disk wind. A nearly edge-on two-dimensional disk model fits the spectral energy distribution (SED) and gives a column of dense warm gas along the line of sight that is consistent with the absorption data. These data illustrate the unique potential of high-resolution infrared spectroscopy to probe the organic chemistry, gas temperatures, and gas kinematics in the planet-forming zones close to a young star.
Free Keywords:Infrared: ISM; ISM: individual (IRS 46); ISM: Jets and Outflows; ISM: Molecules; Stars: Planetary Systems: Protoplanetary Disks; Stars: Formation
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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